In the above described HEV, such as disclosed in Japanese Patent Application Unexamined Publication No. 2010-179865, a so-called one-motor, two-clutch, parallel hybrid vehicle is known in which a motor/generator is interposed between the engine and driving wheels, and the power transmission path between the engine and motor/generator may be selectively established by a first clutch, while the power transmission path between the motor/generator and the driving wheels may be selectively releasable by the second clutch.
HEV may select an EV mode by releasing the first clutch with the second clutch engaged so that the vehicle is driven by the motor/generator only. The HEV may alternatively select a HEV mode by engaging both the first and second clutches so that the vehicle runs under a collaboration of the engine and motor/generator.
In this one-motor, two-clutch, parallel hybrid vehicle, during an operation of EV mode selected at low load, low rotation engine speed condition, in response to an increase in required driving force (required acceleration) such as upon an accelerator pedal depression operation by the driver, for example, when it is determined that the motor/generator would not suffice to provide the required driving force (or required vehicle acceleration), a change or switch over to an HEV mode will be initiated for a coordinated control by both the engine and motor/generator
When staring the engine at this switching of the control mode from EV mode to HEV mode, the first clutch, which has been released during EV mode, is now engaged, and motor torque from the motor/generator will start the engine.